1. Field of the Invention
This invention relates to apparatus for remote control of a plurality of subsea devices, and more particularly to apparatus for individual control of a relatively large number of subsea devices using only a few electrical and hydraulic source lines from a surface control unit to the seafloor.
2. Description of the Prior Art
The production of gas and oil from offshore wells has developed into a major endeavor of the petroleum industry. Wells are commonly drilled several hundred or even several thousand feet below the surface of the ocean, substantially below the depth at which divers can work efficiently. The wells are often located in clusters with production lines extending from each of the wells to a production riser base on the seafloor, then upward to an offshore production platform. The operation of the wells must be controlled from the production platform or from a surface vessel. The testing, production and shutting down of each of the subsea wells is regulated by a subsea Christmas tree which is positioned on top of the subsea wellhead. The Christmas tree includes a plurality of valves having operators which are biased to a non-active position by spring returns, and it has been found convenient to actuate these operators by hydraulic fluid which is directly controlled from the production platform. For this purpose, a plurality of hydraulic lines are commonly run from the surface platform to the wellhead to open and close these valves, and to actuate other devices in the well and the wellhead during installation, testing and operating the subsea well equipment, and also during workover procedures being performed on the well.
Some of the more extensive production fields include a plurality of templates each having several wells thereon and a plurality of individual or satellite wells each having a subsea tree mounted atop the well. The wells may be connected to a plurality of flowlines which are coupled to a production platform through a riser base and a production riser. There are numerous valves and connectors on the trees, templates and riser base which must be controlled in an orderly, precise and fail-safe manner. Prior art control systems have used hydraulic control and pressure lines between the production platform and the individual valves and connectors with a conferral line for each valve or connector to be controlled. As systems become larger, the number of these control lines becomes too large to be handled in a multi-hose bundle and costs become unreasonable.
Other prior art control systems include electrohydraulic operators having electrical control lines to the operators which control hydraulic fluid to open and close valves. Such prior art systems have not achieved a high degree of confidence or use because of the large wire connectors required and due to problems in sealing and providing trouble-free electrical connectors.
One prior art control system which uses total hydraulic control for operating a large number of subsea operators using only a few lines between a surface control center and the seafloor has been developed. The system called matrix switching is disclosed in a copending patent application Ser. No. 101,993 filed Dec. 7, 1979, by the inventor of the present invention.